1. Technical Field
The present invention relates to a hydrogen generator using a steam-reforming reaction, and, more particularly, to a heat exchanger-integrated hydrogen generator for producing hydrogen by a steam-reforming reaction using hydrocarbons as a raw material, in which a pressure loss induction structure for artificially reducing the pressure of exhaust gas is provided between a combustion unit and a exhaust gas discharge pipe, thus improving the uneven heat transfer of the exhaust gas supplied to reactor tubes.
2. Description of the Related Art
Generally, a fuel cell is an electrical generating system for simultaneously generating electricity and heat by converting chemical energy into electric energy by the electrochemical reaction of hydrogen and oxygen.
It is predicted that such a fuel cell will replace an internal combustion engine because it has excellent energy efficiency. Therefore, in the near future, the stable supply of hydrogen will be an essential factor in the use of a fuel cell as a future source of alternative energy.
As methods of supplying hydrogen to a fuel cell, a method of producing hydrogen by electrolyzing water and a method of producing hydrogen by steam-reforming a hydrogen-containing raw material are used.
In this case, all kinds of hydrocarbons, such as natural gas, liquefied petroleum gas (LPG), naphtha, gasoline, kerosene and the like, can be used as the raw material of a steam-reforming reaction. Further, the steam-reforming reaction is conducted at high temperature in the presence of a catalyst.
Therefore, there must be a catalyst in the place in which a steam-reforming reaction takes place, and the heat necessary for the steam-reforming reaction must be supplied thereto.
Conventionally, in order to supply the heat necessary for a steam-reforming reaction, a method of burning fuel to generate heat and then transferring the heat to a hydrogen generator has been used. However, this method is problematic in that efficiency is decreased because heat loss occurs due to the increase in size of an apparatus and the transfer of high-temperature exhaust gas.
Recently, in order to solve the above problem, the inside of a hydrogen generator was divided into two regions, and then one region was used as a steam-reforming region (steam-reforming unit), and the other region was used as a combustion region (combustion unit) for generating the heat necessary for a steam-reforming reaction.
In this case, the catalyst of the steam-reforming unit is mostly located in a catalytic reactor tube having a small diameter, and several catalytic reactor tubes are symmetrically disposed around a heat source depending on the capacity and size of a hydrogen generator.
Further, the heat generated from the combustion unit is transferred to the catalytic reactor tube by the radiation or convection of exhaust gas, and is then used in a steam-reforming reaction.
However, in the heat transfer using exhaust gas, heat cannot be evenly transferred to the catalytic reactor tube because exhaust gas flows unevenly, so that the catalytic reactor tubes are not sufficiently supplied with heat, with the result that a steam-reforming reaction cannot be conducted easily, thereby deteriorating the total performance and efficiency of a reactor. This phenomenon will be described in detail as follows.
Generally, in order to improve thermal efficiency, high-temperature exhaust gas undergoes an exhaust gas recovery process using a heat exchanger several times even after it is discharged from a reformer. For this purpose, exhaust gas gathers at an outlet and is then transferred to a heat exchanger. In this case, exhaust gas moves along the shortest path between a combustor and an outlet. Therefore, as shown in (A) of FIG. 1, a reactor tube which is located relatively far from an outlet does not frequently come into contact with exhaust gas, and thus the amount of the heat transferred from the exhaust gas to the reactor tube decreases.
When heat is unevenly supplied to reactor tubes due to the uneven flow of exhaust gas, there are the following problems. First, when the temperature of some of the reactor tubes does not reach the target temperature, the steam-reforming reaction in the relevant reactor tubes is conducted to a degree lower than the designed value, so that the production of hydrogen decreases and the concentration of unreacted methane in a product increases, thereby directly decreasing the efficiency of a hydrogen generator and increasing the cost for separating a hydrogen purifier necessarily provided at the rear end of a hydrogen generator. Second, when exhaust gas flows unevenly, some of reactor tubes may be heated above their set value, and, when they are exposed to high temperature for a long period of time, a reactor is damaged by the creep of the material of the reactor or by the corrosion of the metal attributable to reformed gas, with the result that the durability of a hydrogen generator decreases. As described above, the uneven distribution of exhaust gas causes the problems of the efficiency of a hydrogen generator being decreased at low temperature and the durability thereof being deteriorated at high temperature. These problems must be solved in order to improve the performance of a hydrogen generator.